1. Technical Field
The present invention relates to a light emitting device and an image display apparatus.
2. Related Art
A head-mounted display (HMD) is known as a display apparatus which directly irradiates the retina of the eyes with laser and allows a user to visually confirm an image.
In general, the head-mounted display includes: a light emitting device which emits light; and a scanning unit which changes an optical path so that the emitted light is scanned on the retina of a user. By the head-mounted display, the user can visually confirm, for example, both a background color of the outside and the image which is drawn by the scanning unit at the same time.
However, in the head-mounted display, since the retina is irradiated with the light emitted from the light emitting device, it is necessary to consider that the retina does not get damaged by the light. In general, safety is secured by limiting an output of the light emitting device so that an amount of the light emitted from the light emitting device does not exceed regulatory limits.
In JP-A-6-151958, in order to control a light emitting output, a light emitting device which is provided with a resistor which controls a current that flows in a light emitting element is disclosed. In the light emitting device, since an element having a characteristic of increasing a temperature and a resistance value is used as the resistor, even if the temperature of the light emitting element increases by self-heating or changing of the ambient temperature, and light emitting efficiency of the light emitting element deteriorates, it is possible to increase a ratio of the current which flows in the light emitting element by making a configuration in which the current that flows in the resistor is reduced according to the temperature increase in the light emitting element. For this reason, it is possible to compensate for the deterioration of the light emitting efficiency, and to always obtain a predetermined light emitting output.
However, in the display apparatus described in JP-A-6-151958, it is possible to prevent the light emitting output from being largely deteriorated, but it is not possible to prevent the light emitting output from being largely increased. For this reason, if a failure or the like is generated on a current supply circuit, and the current becomes too high, there is a concern that the light emitting output exceeds a presumed range.